Soil micronutrient availability after compost addition to St. Augustine grass
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Compost application to turf grasses can increase dissolved organic matter and nutrient levels in soil but may also enhance leaching and runoff losses. The objectives of this study were to determine the influence of composts on soil organic matter and accumulation of DTPA-and water-extractable Mn, Fe, Cu, and Zn in St. Augustine Grass [Stenotaphrum secundatum (Walt.) Kuntze] turf. Composts increased soil organic C (SOC) soon after application, but no further increases occurred beyond 11 months. In contrast, dissolved organic C (DOC) increased from 3 to 29 months after application, indicating contributions from decomposition of composts and St. Augustine Grass residues. Dissolved organic C was 75, 78, and 101% greater 29 months after application of 0, 80, and 160 Mg ha1 of compost, respectively, than before application. While DTPA-extractable Mn and Cu increased from 0 to 29 months, Fe and Zn decreased and were often below background levels. By 29 months, DTPA-extractable Mn and Cu for soil receiving 160 Mg ha1 increased 291 and 3972%, while Fe and Zn decreased 8 and 13%, respectively. Furthermore, water-extractable Mn, Fe, Cu, and Zn decreased 67, 78, 75, and 22%, respectively, by 29 months for soils receiving 160 Mg ha1 of compost. Thus, only DTPA-extractable Mn and Cu accumulated in surface soils receiving composts. Soil pH had more influence on water-extractable than DTPA-extractable micronutrients, as water-extractable micronutrient concentrations decreased while soil pH increased after compost application. Soil organic C, DOC, and DTPA-extractable micronutrients exhibited considerable seasonal variation. Decreases in SOC, DOC, and DTPA-extractable Mn and Cu occurred during winter dormancy after high levels of precipitation. The formation of DOC-micronutrient complexes and leaching following precipitation events likely explain seasonal fluctuations in micronutrient concentrations. Similar trends in micronutrient concentrations were observed for both compost-amended and unamended soils, indicating that seasonal variation was more directly related to growth stages of St. Augustine Grass, precipitation, and subsequent effects on DOC, than compost application. In fact, composts only influenced the magnitude of micronutrient response to application. 2007 by The JG Press, Inc. All rights reserved.
